The Study of the Universe

• Scientists are explorers. Some travel to previously unknown regions, as did Charles Darwin to the Galapagos Islands, Robert Ballard to the floor of the Atlantic Ocean, and Jane Goodall into the rainforests of Africa.

• Other scientists stay home and use instruments as a means of discovery, such as using a microscope to reveal the world of tiny creatures in a drop of pond water.

• To study the universe, scientists pursue both methods of exploration, and up until recently, staying home was the only option.

• Using telescopes and the power of their own thought and imagination, earthbound scientists observed and learned an amazing amount about our solar system and beyond.

• Evidence found in caves, tombs, and on pottery shows that people studied astronomy thousands of years ago, making astronomy one of the oldest sciences.

• Today’s technology has opened the boundaries. Humans have walked on the moon and space probes have toured some of the planets in our solar system – stuff that was once fantasy and science fiction!

Space Walk

Space Station

Phoenix on Mars

Probe on Jupiter

• The universe is everything that physically exists, including all matter, energy and space.

•The study of what is beyond the earth is called astronomy.

What Our Ancestors Saw• For thousands of years, the sky has been

a source of constant, predictable information.

• Long ago, people watched the sky to tell the time of day, the date, the weather, their position on the earth, and when the tides would be higher or lower than usual.

• Many first nations groups noted that the appearance of certain patterns of stars marked the changing of the seasons. This helped than determine when to plant and when to harvest crops.

•Stonehenge, a monument made of huge stones placed in a circle, is a reminder of how important celestial observation was to ancient civilizations.

•It can still be used to calculate and predict celestial motions.

• Celestial bodies is a term for any object that exist in space, such as the sun, the moon, and the stars.

• Farmers took their cues from the changes in celestial bodies, to plant and harvest crops.

• Sailors navigated by the stars.

• Political and religious leaders often made their decisions based on the information they received from those who studied the sky (astronomers).

• During the time of the Roman Empire, the services of astrologers were especially in demand as people believed their destinies could be foretold by the stars.

• Navigation by stars was a valued skill for commerce and trade.– Prince Henry of Portugal, nicknamed the

navigator, set up a school for sailor and was an important figure in Europe’s worldwide explorations.

• Around the world, cultures and civilizations built observatories, created astronomical calendars, and developed the mathematics to predict planetary motion, eclipses, tides, and seasons.

Ancient China

An Ancient Chinese Astronomical Observatory

The water powered clock rotated the instruments in time with the daily motion of the stars.

• Many different cultured had their own accounts about how celestial bodies were formed.

• In Hindu mythology, one story tells of seven wise men who married seven sisters. – Six of the women divorced their husbands and moved

to another location. The six sisters all lived together in the northern sky. They became Pleiades.

– The seven men became the seven stars of the big dipper.

– The one wife who stayed with her husband became the star called Alcor, and remains by the side of Mizar in the crook of the Big Dipper’s handle.

• An asterism is a distinct star pattern.

• A constellation is an officially recognized grouping of stars.

• Cassiopeia• Perseus• Orion• Gemini• The Dippers

• When you look at a constellation, you may not see the shapes that people in ancient times saw.

• Today, rather than showing diagrams of animals or people, many books simply show the shapes to represent the constellations.

• Constellations have been used for thousands of years as calendars, timekeepers, and direction finders by people traveling in unknown territory – both on land and at sea.

A Star Map

• A star map of the night sky shows the relative positions of the stars in a particular part of the sky.

• A planisphere is a very useful type of star map that displays only those stars visible at a given date and time.

• Historically, people formed these star patterns using their imagination to link up stars in the sky. Different cultures linked the stars in different ways.

• The Ancient Greeks thought that the stars that make up Orion depicted a great hunter.

• Some First Nations in North America thought the same stars looked like a canoe floating down a river.

Orion

The Celestial Movie• Imagine that a special camera pointed at the sky

was set up where you live.• For a whole year the camera recorded the

movements of objects in the sky on one continuous video.

• If you play the video back on your T.V. in very fast motion you would see…

• Clouds - various shapes and shades, moving across the sky in the same direction as the daily wind. Clouds would form and break up rapidly. And you may notice that clouds are not very far away. (clouds may be more earthly than celestial).

• The moon is much further away and it’s motion is much more regular. It travels in a westward path across the sky. It appears to be changing shape – waxing from a thin crescent, through a half circle, to a full moon, then waning to a sliver again.

•A moon is a type of satellite, a celestial object that travels around a planet in a closed path, called an orbit.

• The moon is non-luminous and we can only see it when sunlight reflects off its surface.

• The sun is much more dependable. The sun has no phases and it seems to rise at nearly the same time and place as the previous day. If you were to keep careful track though, you would see that it rises a bit later in the winter months, but earlier in the summer months.

•The sun is a star – an enormous ball of hot, glowing gases.

•Compared to other stars, the sun is about average in size, but does have a mass 340 000 x that of earth!

•The sun appears so much brighter than other stars in the sky because if its proximity to the earth.

• Most stars, constellations and asterisms rise in the east and set in the west, but not all.

• Some remain visible all night long, everyday of the year, never rising or setting.

• Careful observation would also show that the stars rise four minutes earlier each night, getting out of sink with the sun. But by getting out of step with the sun, the stars in the night sky reveal seasonal patterns.

• While the stars are generally unchanging, you may notice five other objects that appear to be wandering through the constellations.

• The Greek word for wonderer is planets, and the five wondering planets are Mercury, Venus, Mars, Jupiter, and Saturn.

• A planet is a large celestial object that travels around a star. There are eight planets travelling around our sun.

• Each planet differs for the others in size, composition, atmosphere.

• Mercury, Venus, Mars, Jupiter, and Saturn slowly change position from night to night, two of them staying near the sun (Venus and Mars). When they are visible, they are best seen in the early evening or early morning.

• The four planets closest to the sun are called the terrestrial planets, with hard, rocky surfaces.

• The next four planets are composed mainly of gases and liquids and are known as the gas giants

•Planets are non-luminous, which means they do not produce their own light.

•They reflect light from luminous objects such as the sun and other stars.

Position of Mars during a period of retrograde motion. Each point represents the planet’s new position every 10 days over the retrograde period.

Mars, Jupiter, and Saturn seem to wonder eastward through the night. About once a year they loop back briefly in retrograde motion before continuing eastward.

Looking up at the night sky, you can see as many as 2000 stars. Some of the brighter pinpoints of light are planets

• Within the universe are huge collections of stars, gas, dust, and planets. These are called galaxies and there are billions of galaxies scattered throughout the universe!

• The earth is part of the Milky Way galaxy, with more than 200 billion stars (including the sun).

Modeling Celestial Motion

• Early people’s search for an explanation for the motion of the stars is part of the ongoing human desire to understand the world we live in.

• When we pay attention to what is going on around us, we begin to see patterns. The next step is to understand the patterns. So we come up with a basic idea, or theory, that leads us to develop a model.

• Models are useful tools to aid inquiry and test ideas.

Two Models to Explain the Motions of the Sun, Moon, Planets and Stars

• The Earth-Centered Model, also called the geocentric model, was based on ideas of the Greek philosopher Aristotle.

• The Heliocentric Model is the sun centered model that is accepted today.

Earth Centered Model

• All celestial bodies seem to move across the sky from east to west during the day and night, revolving around the earth. It was not hard for early observers to imagine earth being at the center of a gigantic sphere on which the sun, moon, and planets were attached.

• Aristotle used his ideas of circles and spheres to create the geocentric model.

• The earth-centered model provided a means of predicting dates and times of when the celestial bodies rose and set.

• Ultimately though, this model required up to 55 different inner spheres to account for the observed motions.

• A particular difficulty was explaining why three planets sometimes reversed their direction.

Sun Centered Model

• In the early 1500’s, Nicholas Copernicus proposed a different model, a more simple one, to explain the view from the earth.

• He proposed that, rather than earth being fixed and the sun traveling eastward through the stars, that the sun was fixed and the earth traveled westward around the sun.

• The solar plane is an imaginary, flat disk extending out from the sun’s equator on all sides, along which, the planets orbit the sun.

Galileo

• It was an Italian astronomer, Galileo, who found some persuasive evidence to support the heliocentric model.

• Using an early telescope, Galileo made several exciting discoveries.

• Venus exhibited phases just as the moon did.• The sun has spots.• There are mountains on the moon’s surface• Saturn has rings• Jupiter has four moons

More Work on Copernicus’ Model

• Copernicus’ model was an improvement over the heliocentric model, but there were still some things that could not be explained.

• Johannes Kepler came up with some fancy calculations and was able to accurately predict if planetary orbits were ellipses and not circles.

• Sir Isaac Newton also contributed to the model with his law of gravitation, which states that there is a gravitational pull between all objects. This forces gets stronger as objects get closer to each other.

1781

• There was great excitement in 1781, when a new planet was discovered – Uranus.

• Using the sun centered model and Newton’s law, astronomers were able to predict the position and orbit for another planet – Neptune.

Surveying The Solar System

• The invention of the telescope revealed a lot about the night sky, but it was when scientists began applying their knowledge of gravity and Newton’s laws to space technology, that our understanding of the solar system really expanded.

• New types of telescopes were developed to see further and one was even placed in orbit (Hubble Telescope) to see even further.

• Space Probes, such as Venera, Solar Observer, Pioneer, Viking, Voyager, and Pathfinder, have been dispatched to visit the sun and planets.

• These probes send back pictures and measurements of planet orbits, surfaces, atmospheres, and moons.

Probe Name

Launch Year

Arrival Year

Details

Magellan 1989 1995 Mapped Venus using radar waves before crashing into planet.

Galileo 1989 1995 Flew past asteroids to explore Jupiter and its moons.

Pathfinder 1996 1997 Two probes were sent to study Mars. Pathfinder landed on Mars and sent a rover to explore the surface.

Cassini 1997 2004 Probe studying Saturn and its largest moon. Expected to operate until 2008.

Surveyor 1998 1999 Will study the climate of Mars and search for water.

The Sun

• The sun is a huge globe of mostly hydrogen (73%), the lightest of the gases. There is also 25% Helium.

• It is about 1.4 million kilometers in diameter (110 times the diameter of the earth).

• The sun is so hot (15 000 000 oC) that the gas glows and it is this light that speeds through space to reach and warm the earth.

The sun is all “atmosphere” because it is all gas. When people refer to the “surface” of the sun, they are referring to the outside glowing region called the photosphere.

• The surface of the sun (photosphere) constantly churns and writhes.

• Solar prominences are streamers of glowing gas that arch into space.

• Some regions on the sun are cooler than their surrounding and therefore appear to be darker. These are known as sun spots.

• Near sun spots are where violent solar flares occur, sending streams of high energy subatomic particles into space. This outflow of particles is known as the solar wind and can have a great affect on the activities of earth.

The Ecliptic• The sun appears to move against the

constellations of the celestial sphere.

• The path take by the sun (as it appears to us on earth) across the celestial sphere is called the ecliptic.

• This apparent motion of the sun is caused by Earth’s revolution around the sun. The earth’s rotation causes celestial objects to move across the sky from east to west.

Day and Night

• The sun spins one complete rotation around its axis in 24 hours. The part that faces the sun is experiencing day.

Years and Leap Years

• In the time that it takes the earth to make one complete revolution around the sun, it has rotated on its axis 365 times. There are 365 days in a year.

• Using a calendar with 365 days every year would result in a loss six hours per year. Adding a day ever four years fixes the problem.

The Four Seasons

• To understand why seasons change, consider the earth’s orbit around the sun, as well as the earth’s orientation in this orbit.

• The earth is spinning or rotating on its axis (an imaginary line from the North pole to South pole) while orbiting around the sun.

• The axis of rotation is tilted with respect to the plane of orbit.

• When the earth is oriented as it is in the picture, the sun’s rays that strike earth’s surface perpendicular to the surface are not hitting the equator, but instead are hitting just north of the equator.

• In this orientation the Northern hemisphere receives more sunlight than the Southern hemisphere. This is summer in the North.

• As the earth progresses around the sun, the angle between the axis of rotation and the orbital plane stays the same.

• When earth, moves counterclockwise around the sun, summer changes to fall in the Northern hemisphere. The sun’s rays strike the equator perpendicular to the surface so the amount of sunlight that reaches the two hemispheres is equal.

• Three months later, the sun’s rays strike perpendicular to the earth’s surface just south of the equator. This causes summer in the Southern hemisphere and winter in the North.

• Finally, when the most intense sunlight is once again at the equator, spring has arrived to the Northern hemisphere.

The Planets

• All the planets differ from one another in size, motion, composition, density, and temperature. No two are exactly alike.

• The inner planets (Mercury, Venus, Earth, and Mars) are sometimes called the terrestrial planets because of their terrestrial (rocky) composition.

• Jupiter, Saturn, Uranus, and Neptune are the outer planets and are similar because of their gaseous composition.

• Pluto is in a category all by itself. It was recently decided that Pluto is not actually a planet. It has a strange orbit and a tiny size.

A way to Compare Planets

• Studying planets in a meaningful way, first requires a useful scale with which to make comparisons.

• A standard approach in astronomy is to compare the planets to the one we know the best – the earth!

• One earth diameter is 12 750 km• Venus’ diameter is 12 100 km (0.95 of earth)• Jupiter’s diameter is 143 200 km (11.2 of earth)

JupiterSaturn Uranus Neptune

EarthVenus

• Similarly, a planet’s mass (amount of matter in an object) can be expressed in terms of earth-mass.

• And density (the amount of matter that occupies a particular space, mass divided by volume) can be expressed in terms of earth-density.

• Surface temperatures can be compared and degrees Celsius is the standard scale.

• Because distances in astronomy are so immense, scientists came up with a different way to compare the measurements.

• To study distances in the solar system, astronomers use astronomical units (AU).

• One AU equals the earth’s average distance to the sun.

• So earth is 1 AU (149 599 000 km) from the sun• Mars is 1.5 AU (228 000 000) from the sun.

• Scientists also measure distance in light years.

In order to be a planet…

• The celestial object must• Be in orbit around a star• Have enough mass to be pulled into a stable

sphere shape by gravity• Dominate its orbit (mass must be greater than

anything else that crosses its orbit.

Dwarf Planets

• Pluto was considered the ninth planet from 1930 to 2006. It is now considered a dwarf planet, which orbits the sun and does have a spherical shape, but does not dominate its orbit.

Other Solar System Bodies

• Moons

• Asteroids

• Comets

• Meteors and Meteorites

Moons• Large natural objects that revolve around

planets are called satellites, or moons.• Several planets have more than one

moon.• The most famous satellite is the moon that

orbits the earth.• It has a diameter that is ¼ that of the earth.• It has been visited many times.• It has no atmosphere.• Its surface has many hills and valleys, as well as

craters.

• The moons of other planets were discovered after the invention of the telescope.

• In 1610, Galileo looked at Jupiter through his telescope and became the first person to see the four moons.

Planetary Moon Count

Planet Number of Known Moons (1998)

Mercury 0

Venus 0

Earth 1

Mars 2

Jupiter 16

Saturn 18

Uranus 17

Neptune 8

(Pluto) 1

Phases of the Moon

• The moon is illuminated by the sun, but the illuminated side does not always face the earth, which mean that we see different amounts of the lit side as the moon orbits the earth.

• Over a period of about four weeks, the amount of illuminated surface of the moon we see (phases) follows a predictable pattern.

• The eight phases of the moon make up the lunar cycle.

•The lunar cycle starts with a new moon. The moon is not visible from earth as the side that is illuminated is facing away.

•After this phase, the illuminated portion of the moon increases (waxes).

•A full moon appears as a lit circle in the sky with the illuminated surface facing the earth.

•The second half of the lunar cycle has the illuminated portion decreasing (waning) until the moon can no longer be seen, starting the cycle over again.

Eclipses

• Eclipses are spectacular astronomical events that occur when the position of one celestial object blocks the view of another celestial object from earth.

Solar Eclipses

• When the moon is aligned between earth and the sun, it blocks the sun from being observed from earth – a solar eclipse.

The sun has a diameter 400 times greater than the moon, but it is also 400 times farther from the earth so it appears to be the same size in the sky

•A partial eclipse occurs when the moon does not cover the entire sun.

Lunar Eclipses

• A lunar eclipse occurs when the earth is positioned between the sun and the moon. This casts a shadow on the moon.

• A total lunar eclipse is when the entire moon passes through the earth’s shadow.

• A partial eclipse is when only part of the moon passes through the earth’s shadow.

Partial Eclipse

Total Eclipse

Asteroids

• Voyager 2 journeys to the outer planets making tremendous observations and measurements that have changed our view of the solar system.

• The trip was not without risk though. The craft had to pass through a region of millions of asteroids located between Mars and Jupiter.

• These objects are also known as minor planets. These irregularly shaped bodies are made of carbonaceous rock or silicate rock.

• Ceres are the largest asteroid, with a diameter of 1000 km.

Comets• Periodically, comets are visible to the unaided

eye, but are normally detected by telescopes.• These objects are made up of mainly dust and

ice. Scientists have labeled them “dirty snowballs”.

• Occasionally a comet gets bumped from its orbit by the gravitational pull of several objects. This causes the comet to fall toward the sun.

• Material begins to evaporate from its surface, formaing tails that can be thousands of kilometers longs. The tail always points away from the sun because it is pushed by the solar wind.

Halley’s Comet

When it passed through the inner solar system in 1986, Comet Halley was observed by five space probes. The European Giotto Spacecraft showed the first ever close-up pictures of a comet. This one had a nucleus that measured 16km by 8 km.

Meteors• Everyday, earth is bombarded by

thousands of dust and rock fragments from space.

• When they enter the atmosphere, friction causes these particles to heat up and vaporize.

• If the fragments are large enough, however, it sometimes burns up, generating enough light to make it visible. These are called meteors (shooting stars).

Meteor over Northwest De Moines

Meteorites

• Some fragments are either large enough or tough enough that remnants survive and hit the earth’s surface. These are meteorites.

• Scientists use these fragments to study extraterrestrial material.

Satellites

• Earth has one natural satellite orbiting around it – the moon. Earth has many other satellites circling around in at different altitudes, but these are all man made.

• Human-occupied spacecrafts, such as the space shuttle and the space facilities (International Space Station ISS) are artificial satellites.

Navigating the Night Sky• Finding your way around the night sky can

be confusing. The first step is to learn how to describe the location of celestial objects that can be seen with the unaided eye.

• In geography, latitude and longitude are used to pinpoint a place or object on earth. In astronomy, celestial coordinates are called azimuth and altitude.

Azimuth

Azimuth is the horizontal angular distance from North measured eastward along the horizon to a point directly below the celestial body.

Altitude

Altitude is the angular height a celestial object appears to be above the horizon

Astrolabe

•An astrolabe is a historical astronomical instrument used by astronomers, navigators, and astrologers. •Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars

• Developing methods to measure the distance of stars from earth and from each other was a major accomplishment in astronomy.

• It provided a way of estimating the size of the universe and it offered valuable clues about the age of the universe.

Sir Isaac Newton

• In the 17th century, Newton calculated that Sirius (one of the brightest stars in the sky) is about 1 million times as far from the earth as the sun.

• He compared the brightness of Sirius to the brightness of Saturn and was able to calculate the distance from earth to Sirius.

• This was the first modern attempt to measure distances outside of our solar system.

Measuring with Triangulation

• By using a distance that you know, you can calculate an unknown distance indirectly.

• Triangulation is a method of measuring distance indirectly by creating an imaginary triangle between an observer and an object whose distance is to be estimated.

Surveyors often use simple geometry and trigonometry to estimate the distance to a faraway object.

By measuring the angles at A and B and the length of the baseline, the distance can be calculated without the need for direct measurement.

It is important to know that when measuring distances with triangulation, that the longer the baseline, the more accurate the results.

Using Parallax

• When astronomers use triangulation to determine the distance to a nearby star, they rely on the star’s parallax to provide them with the angles they need to make the necessary measurements.

• Parallax is the apparent shift in position of a nearby object when viewed from two different points.

• The closer an object is to the observer, the larger the parallax.

• Hold a pencil vertically in front of your nose and concentrate on some far-off object—a distant wall, perhaps. Close one eye, then open it while closing the other. You should see a large shift of the apparent position of the pencil projected onto the distant wall—a large parallax.

• In this example, one eye corresponds to point A, the other eye to point B, the distance between your eyeballs to the baseline, the pencil to the planet, and the distant wall to a remote field of stars.

• Now hold the pencil at arm’s length, corresponding to a more distant object (but still not as far away as the even more distant stars). The apparent shift of the pencil will be less.

• By moving the pencil farther away, we are narrowing the triangle and decreasing the parallax (making accurate measurement more difficult). If you were to paste the pencil to the wall, corresponding to the case where the object of interest is as far away as the background star field, blinking would produce no apparent shift of the pencil at all.

The observer at point A sees the planet at apparent location A’relative to those stars. The observer at B sees the planet at point B’.

If each observer takes a photograph of the appropriate region of the sky, the planet will appear at slightly different places in the two images.

The planet’s photographic image is slightly displaced, or shifted, relative to the field of distant background stars. The background stars themselves appear undisplaced because of their much greater distance from the observer.

This apparent displacement of a foreground object relative to the background as the observer’s location changes is known as parallax.

• To measure distances from earth to celestial bodies, the longest base line we can use without leaving the earth is the diameter of the earth’s orbit.

• Sightings have to be taken six months apart – the time it takes to move from one end of the orbital baseline to the other.

• Calculating a star’s distance from the earth using parallax and triangulation.

• In January, the nearby star (A) apprears to line up with (B).

• In June, it seems to line up with (C).

• A appears to move in the sky (parallax).

• Stars B and C are so far away that they do not appear to move.

• This provides the angles needed to use triangulation.

Light Years

• The image on the previous square is very much out of scale.

• The nearest star to earth is Proxima Centauri and it lies nearly 272 000 astronomical distances from the sun.

• Because inter-stellar distances are so much greater than solar system distances, astronomical units are impractical to use – as impractical as it would be to measure the distance across Canada in millimetres!

• Astronomers measure distances in light years.

• A light year represents the distance that light travels in one year, and equals 63 240 AU.

• On this scale, Proxima Centauri is 4.28 light years away.

The Properties of Stars

• If you were to look at the sky on a night when the moon is not visible, you may notice how stars differ in their brightness. Some are dazzling points of light while others are very faint.

• If you were to use a pair of binoculars or a telescope, many stars become visible.

• A telescope is a light collector. The huge lens or mirror is like a giant eye that collects all the starlight that falls on it and concentrates it in the eyepiece.

• Astronomers have inferred a great deal from starlight about important properties of stars: brightness, colour, temperature, composition, mass and size.

Properties of Light

• Before the 1900’s, scientists thought that light behaved solely as a wave. This belief changed when it was later discovered that light also has particle-like characteristics. Still, many of light’s properties can be described in terms of waves.

Visible Light• Visible light is a kind of electromagnetic

radiation. Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space.

• Other kinds of electromagnetic radiation are x-rays, ultraviolet and infrared light, microwaves, and radio waves.

• Together, all the forms of electromagnetic radiation form the electromagnetic spectrum.

• What we perceive as color is actually different wavelengths. The shortest waves are gamma rays and the longest waves are radio waves.

• Visible light falls in between. Red light has the longest wavelength or the colors in the spectrum, and violet has the shortest wavelength.

• The visible portion of the electromagnetic spectrum is called the continuous spectrum because the component colours are distinct. The colours appear to be smeared together, but this is not the case.

• When atoms absorb energy, a pattern of distinct coloured lines separated by spaces of varying lengths are observed. This line spectrum can be observed for hydrogen, as well as other atoms.

The discrete coloured lines of this spectrum are characteristic of hydrogen atoms. No other atoms display this pattern.

The Brightness of Stars

• One star can seem brighter than another because it is larger or because it is closer to earth, but not all the closest stars are necessarily the brightest.

• Once astronomers understood the distances, they realized that luminosity is a property of the stars themselves.

• Luminosity of a star is measured by comparing it with the luminosity of the sun.– The sun’s luminosity is 1.– Sirius has a luminosity of 22, which means it

gives off 22 times more energy each second than the sun.

– The sun appears brighter because it is much closer to earth (sun is 0.000 016 ly away whereas Sirius is 9 ly away)

• Luminosity is a measure of the total amount of energy a star radiates per second.

• Headlights and flashlights appear brighter when they are closer. – When a light source is far away, the light

spreads out over a large area and becomes more diffuse.

– When a light source is close, the light is concentrated in a small area.

Temperature of Stars

• Although the stars in the night sky look like small points of white light, they are in fact a range of colours. A relatively hot star appears bluish while others that are cooler are orange-red.

• Astronomers use colour to infer the star’s surface temperature. The colour of starlight is identified in terms of wavelengths in the electomagnetic spectrum to give a measuring tool for star temperature.

Colour and Temperature of some Stars

Colour Temperature Range (oC) Examples

bluish 25 000 - 50 000 Zeta Orionis

bluish-white 11 000 - 25 000 Rigel, Spica

whitish 7 500 - 11 000 Vega, Sirius

yellowish-white 6 000 - 7 500 Polaris, Procyon

yellowish 5 000 - 6 000 Sun, Alpha Centauri

orangish 3 500 - 5 000 Arcturus, Albebaran

reddish 2 000 - 3 500 Betelgeuse, Antares

Composition of Stars

• Colour tells more about a star than its temperature. Analysis of starlight indicates a star’s composition.

• To analyze the light, astronomers use a spectroscope to separate light into bands of different colour.

• If some of the wavelengths of light disappear, it is because it has been absorbed by gases in the star’s atmosphere. Each element leaves a unique dark band on a spectrum so from the spectrum, astronomers can infer the elements that make up a star’s atmosphere.

The Size of Stars

• Once scientists determine the luminosity and temperature they can calculate the radius of the star, which come is all sorts of sizes.

The Mass of Stars

• Mass was a bit more difficult to determine. More than half the stars discovered are binary stars, which means there are two single stars orbiting one another.

• By knowing the size of the orbit and the time it takes the two stars to complete one orbit, astronomers were able to calculate the mass of each star.

The Hertzsprung-Russell Diagram

• As astronomers learned more about the properties of stars, they began to search for patterns in the data.

• Graphing is a very useful way to identify patterns.

• In the 1920’s , Hertzsprung and Russell plotted the luminosity and temperature/ colour of several stars.

• Generally, for stars that are at equal distances from the Earth, the more luminous a star, the brighter it is.

• The luminosity of stars is affected not only by temperature but also by size. – The most luminous stars would be those that

are large and hot. – Those that are the least luminous would be

small and cool.

• The colour of a star is determined by its surface temperature, which is illustrated on the Hertzsprung-Russell diagram

• Astronomers noticed that 90% of stars plotted on the H-R diagram fit into a diagonal band, which they called the main sequence.– In the lower right part of the sequence are the

cooler, reddish, dim stars.– In the top left are the luminous, hot, bluish

stars– There are some dim hot stars and luminous

cool stars as well, but they are off the main sequence.

The Lives of Stars

• It is easy to believe that stars are merely pinpricks of light, fixed forever in the sky.

• The approximately 6000 stars visible to the unaided eye seem unchanging in pattern, motion, and shape.

• New technologies, such as the telescope, gave astronomers the ability to see further and as a result, they had to develop new explanations for what they saw.

• The discovery of the remote planets in our solar system was just the beginning of the expanding view of the universe.

• By combining telescopes and photography, astronomers were able to collect and record light from objects too faint to be see with the unaided eye.

• These technological improvements revealed not only a few thousand stars, but a billion of them!

• Every star has a beginning, a middle, and an end.

• The life of a star may last billions of years. Our sun for example, has been around for 5 billion years and is not yet near the end of its life cycle.

The Evolution of Stars

• Newton’s law of gravitation states that an attractive gravitational force exists between all masses, and that this force gets stronger as the two objects become closer.

• Gravity is constantly at work. It is the force that not only helps create and build stars, but that ultimately causes them to die.

Nebulae

• Astronomers speculate that vast clouds of gas and dust, called nebulae, are the birth place of stars.

• It is in those clouds that gravity works to pull inter-stellar material together.

• The accumulating gas causes the temperature in the center to rise and when the temperature reaches 10 000 000 degrees Celsuis, nuclear fusion begins and the star turns on.

Eagle Nebula

For centuries, observers of the night sky could not see more than their earth base telescopes revealed. Space-based instruments have enabled astronomers to improve their view and understand how large and complex the universe is.

Compare the earth-based view of Eagle Nebula with the detailed view obtained by the Hubble Space Telescope. The Hubble image is showing star formation!

Main Sequence Stars

• Once the fusion process begins, it stars to consume the hydrogen fuel and Helium begins to accumulate in the core of the star.

• The interior of the star continues to heat up and this increases in pressure and temperature balances out the gravitational pull towards the center. The result – a stable state!

• The time that a star remains in the stable main sequence phase before moving on to a later phase depends on its mass.

Low Mass Stars

• Low mass stars (red dwarfs) consume their hydrogen slowly over a period that may be as long as a billion years. During that time, they lose significant mass, essentially evaporating.

• In the end, all that remains of them is a very faint white dwarf.

Intermediate Mass Stars

• Intermediate mass stars, such as the sun, consume their hydrogen a little faster than their low mass neighbors – over a period of about 10 billion years.

• When the hydrogen is used up in the core of one of these stars, energy production stops and the core resumes its gravity-driven collapse.

• As the core contracts, the temperature of the core increases and the outer layers of the star begin to expand.

• By the end of this phase, the star can be 10 to 100 times its original diametre!

• When the temperature of the core reaches 100 000 000 degrees Celsius, the helium starts fusing into carbon.

• Because the star has expanded to such an enormous size, the outer layers are much cooler than when the star was a main sequence star. It therefore appears red and is called a red giant.

• Our sun will eventually evolve to this phase – in about 5 billion years!

• Stellar winds peel away gases, eventually revealing the hot inner region of the star. The result is a planetary nebula.

• Over time, a planetary nebula disperses into space, its remnant cooling slowly and losing brightness, eventually becoming a white dwarf.

• White dwarfs cannot shrink any further in size, but their super dense core gradually cools.

• In their final phase, they become nothing more than a black cylinder, called a black dwarf.

Massive Stars

• High mass stars consume their hydrogen very rapidly. Their core gets so hot that the helium can fuse into heavier elements. So much energy is released in this process that the star swells into a super giant.

Supernovas

• Massive stars live short, bright, energetic lives, but their final exit is even more spectacular.

• Once an iron core is achieved, no further fusion processes are available to counteract the force of gravity, and the core collapses.

• As a massive shock wave bursts from the star’s surface as a huge explosion called a supernova!

Neutron Stars

• After the supernova phase, a star has one of two fates, depending on its mass.

• If the remaining core of the supernova is 1.4 to 3 of the sun’s mass, the gravity within it is still capable of crushing the remnant into small, super dense objects called neutron stars.

Black Holes

• Supernova cores that are three times the mass of the sun or more have a more astonishing end. It is believed that they form black holes.

• Black holes are objects that are so compact and dense that not even light can escape.

• Black holes are the most extreme conclusion of gravity’s work in stellar evolution.

Exploring the Cosmos

• Billions and Billions of stars exist, and billions of them are larger than our star in our solar system.

• What is the size of the space that contains all of these stars?

• Is the universe infinite?

• How did it begin?

• Is it still changing?

The Use of Space

• Since 1957, when Sputnik I was sent into space, scientists have been using human-made satellites as important tools in space.

• Orbiting earth, these objects are now used by many countries from all over the world for communication, observation and monitoring, navigating, and mapping.

Apollo 8

• The Apollo 8 astronauts circling the moon in 1968 were the first people to view earth from afar.

• Since that historic mission, many images of earth have been taken, showing how small and fragile earth seems in the vastness of the universe.

• The Hubble Telescope will soon peer into the cores of some galaxies that have quasars and the result will tell us how realistic our theories about these mysterious objects are.

Communication Satellites

• In 1953, Queen Elizabeth’s Coronation was filmed and then rushed over to North America by plane for Canadians to see.

• Nowadays we are able to watch the World Cup Soccer AS IT HAPPENS!!

• The world has become a global village of instant communication, thanks to orbiting satellites.

• Satellites orbiting close to earth take about .5 hours to circle the planet. A moving antenna is needed to track them.

• Geosynchronous satellites are in synchronized orbit with the earth’s rotation – so it makes one complete orbit each time the earth rotates and appears to be motionless over a point on the earth’s surface.

• Canada is a world leader in the development and use of communication satellites.

• On November 10, 1972, Canada’s domestic communication satellite, Anik 1, was launched from Cape Canaveral.

• On February 5, 1973, the Canadian Broadcasting Corporation started network television transmission to Canadians – the first country in the world to use satellites to transmit television!

• More sophisticated Anik satellites have been launched since then.

Observation Satellites

• Observation satellites are used for forecasting weather, carrying out research, and helping ships, aircrafts, and other vehicles determine their exact location on earth.

• Satellites can also be used to measure depths of snow, the extent of ice build-up in arctic waters, and the locations of forest fires.

Forest Fires on the California Coast

• Some observation satellites use spectroscopy to measure air pollution.

• Hot gases emit specific colours of light and cold gases absorb those colours, a satellite can analyze light patterns in the atmosphere to determine how abundant a particular gas is.

• Canadian observation satellites are named LANDSAT and RADARSAT.

• The center for remote sensing in Ottawa maintains two receiving stations for the satellites – one in Prince Albert, SK. and one Gatineau, Quebec.

Global Positioning System Satellites (GPS)

• A small, hand held GPS unit uses satellite technology to find where you are on earth.

• More than two dozen GPS satellites, called NAVSTAR (for navigation and satellite tracking and ranging) are now spread out in high orbit around the earth so wherever you are, there are at least three above the horizon.

Photographing Space

• Satellites can aim their instruments outward from earth and take images far out into space.

• Orbiting above earth’s atmosphere means that the satellite is not affected by the atmosphere, which distorts transmission, and as a result, the pictures taken are much more clear.

Space Travel

• For generations, people have dreamed of travelling to distant parts of the universe.

• In 1969, when Neil Armstrong stepped onto the moon’s surface from Apollo 13, the event marked a major milestone in achieving the dream.

• Robotically-operated space probes have landed on Venus and Mars and have given close up views of the ground on these foreign worlds.

• For several years, the US sent astronauts to Sky Lab, a small space station orbiting earth.

• Space Stations have living quarters, work and exercise areas, and all of the equipment and support systems that humans require to live and work in space.

• In the 1980’s and 1990’s, Russian astronauts lived in the space Station Mir for extended periods of time.

Space Stations

Sky Lab

Mir

• For the last decade, the Space Shuttle has also been carrying astronauts and scientists into orbit.

• A major component of the Space Shuttle is the robotic arm outside the spacecraft that can be manipulated by remote control. The arm was developed by a Canadian company – Spar Aerospace.

• Shuttle crews have used the arm to release and retrieve satellites from the Shuttle’s cargo bay, as well as a rescue mission when the Hubble Telescope was found to be defective after the launch!

• The next major space project is the International Space Station – a joint project between the US, Canada, most of Europe, Russia, and Japan.

• The Space Station will be a permanent lab where scientists can conduct long-term research experiments in space.

• It also might become the site of spacecraft construction and launching.

Careers Involving Space Exploration

• Space exploration is an exciting field for many reasons.

• It requires the application of nearly all areas of science and technology to the goal of discovery and learning.

• It also involves an adventurous spirit and a great deal of resourcefulness and imagination.

• It is an area of human endeavor where international cooperation and exchange is vital if advances are to be made.

Astronaut

• The ultimate space-related career is being one of the individuals to travel beyond the earth’s atmosphere.

• Astronauts must be in peak physical condition to perform demanding tasks required in the small quarters of a space craft.

• Periodically, the Canadian Space Agency advertises for applicants to train for this job.

Satellite Technologist

• Constructing satellites or developing software to manage the satellites and interpret data, there are many links between computer technology and satellite communication.

• Engineers, physicists, mathematicians, chemists, mechanics, computer programmers, and technicians are all members of the satellite teams.

Aerospace Industry Careers

• Architects and trades people in several countries are working on modules of the International Space Station – everything from sleeping quarters to inventing recipes for occupants,

• Workers in the aerospace industry design and build the spacecrafts that explore the solar system and the rockets that lift them off the earth.

Astronomer

• Many major universities have an astronomy department. Astronomers are hired to teach the subject and carry out research.

• Many Canadian universities have excellent astronomical telescopes, and Canadian astronomers share observation time on the world’s great optical and radio telescopes.

Careers in Microgravity Research

• Astronauts living and working in space must cope with the effects of microgravity, which is a condition in which objects in orbit seem to be weightless. In reality, gravity is acting on them, but its effects are reduced.

• Human living in a microgravity environment for prolonged periods of time develop health problems: bones and muscles weaken.

• If we ever want to launch extended trips – to mars maybe, then we need to learn the effects of microgravity on the human body.

Challenges of Space Travel

• A feeling of weightlessness (page 420)

• Health and other risks (page 421)

• Space Junk (page 424)